The invention relates in general to means and a method for applying a lateral thrusting force for movement of an assembly, and in particular to means for penetrating earth with a lateral thrust being applied thereto. It is a common problem in both vertical and horizontal drilling to provide sufficient lateral thrust for advancing a drill bit and the like. Prior art devices for supplying lateral thrust have in general been expensive, cumbersome, or unsuitable for a wide variety of applications. Also, directional control of the drilling mechanisms when lateral thrust applying mechanisms have been utilized has been difficult, requiring time-consuming orientation and deviation procedures.
According to the present invention, the problems associated with conventional prior art lateral thrust supplying and direction control providing means are solved. According to the present invention a lateral thrust mechanism is provided which employs elastomers and reinforcing material operated in tension, the unit relying only on stressed membrane strength and flow characteristics, rather than conventional structural design. This allows the device to flow over and around obstacles and to operate in physically deformed conditions which would cause structural failure or at least jamming of conventional hydraulic devices. At the same time, the mechanism according to the present invention can supply large lateral thrust forces both for vertical and horizontal drilling.
A lateral thrust unit according to the present invention takes the form of four hydraulically operated force cells (preferably toroidal) associated with a thrust mandrel (preferably tubular) of a given fixed length. Two of the force cells are lateral force cells, being expandable in the lateral direction, but being substantially of fixed dimension in the radial direction. The combined lateral dimension of the two lateral force cells always remains the same. The other two force cells are radial force cells, being expandable in the radial direction, but having a substantially constant lateral dimension. One radial force cell is disposed between the lateral force cells, while the other radial force cell abuts only one of the lateral force cells.
The cells operate to apply a lateral force by the transfer of the application points of thrust, and not through the expansion and contraction of the units themselves. A typical cycle of operation of the mechanism that would result in the lateral advance thereof (and any drill bit or the like attached thereto), a distance corresponding to the difference between the length of a lateral cell in the expanded and contracted positions thereof, is as follows: With the lead lateral cell expanded, the lead radial cell is expanded to engage the walls of the borehole securely, and effectively anchor itself to the borehole at that point. The lead lateral cell is then deflated, and the rear lateral cell correspondingly expanded to move the rear radial cell forward a distance corresponding to the difference in length between the rear lateral cell in its contracted and expanded positions. The rear radial cell is then expanded to engage the borehole walls, while the lead radial cell is contracted. Then the lead lateral cell is expanded while the rear lateral cell is contracted, to thereby move the lead portion of the mechanism forward a distance corresponding to the difference in length between a lateral cell in the expanded and contracted positions.
While the thrusting mechanism according to the present invention may take a wide variety of forms, preferably it consists of torodial force cells disposed around a tubular mandrel, and covered by an outer jacket of urethane rubber or the like, four such cells mounted on a mandrel comprising a muscle unit. Each lateral force cell may comprise a toroidal piston and a cylinder (formed by concentric tubes) which are movable with respect to each other, and an inflatable torodial flexible membrane disposed between the piston and cylinder for moving the piston and cylinder with respect to each other. The piston may be spaced from the cylinder along the whole periphery thereof, and the membrane doubled over in the space therebetween. The membrane may be of smaller deflated diameter than the piston, but will always be inflated enough to tension it so that it remains in contact with the cylinder interior walls and the piston. Other forms are, of course, possible, such as a conventional piston and cylinder. Each of the radial cells may be a conventional inflatable member constrained from movement in the lateral direction, but free to move radially. A means can be provided for introducing only a predetermined volume of fluid into the radial cell during expansion thereof. One radial cell, the one between the two lateral cells, will be slidably mounted with respect to the mandrel, while the other radial cell will be fixed with respect to the mandrel.
A plurality of lateral thrust applying members according to the present invention may be disposed together, the force being applied thereby being multiplied. The mechanisms are connected together by means for allowing parallel or non-parallel movement therebetween, such as a pair of steering rings having a plurality (i.e. 4) of inflatable steering cells disposed therebetween. By selective inflation of the steering cells, the elevation and azimuth of the penetrating device can be controlled.
A wide variety of earth penetrating tips and power supply means may be provided for use with an earth penetrating device utilizing the lateral thrust applying mechanism according to the present invention. Drill bits could be utilized, either powered from the surface through a drill string, or powered by down-hole motors or turbines. For soft earth penetration, a compactor may be utilized. According to the present invention, a compactor may be provided having a penetrating tip portion that is movable with respect to a compacting portion, the compacting portion having a plurality of inflatable cells of increasing diameter disposed around a conical rigid member. The cells are dimensioned so that the inflated diameter of one cell is equal to or greater than the deflated diameter of the next largest cell, so that a void formed by one cell may be filled by the next largest cell for further enlargement thereof. During operation, the penetrating tip is moved forwardly with respect to the compacting portion to form a small borehole, a lateral thrust is applied to the compacting portion (with cells deflated), with the tip retracted, to move it as far forward as possible into the area formed by the penetrating tip, the cells are inflated to increase the size of the hole diameter, and then the cells are deflated and the procedure repeated. The pressure applied to the cells is sufficient to cause the surrounding earth to compact upon itself, and may exceed, for example, 5,000 pounds per square inch. Since pressures such as this could exceed the free space rupture strength of the cells, the fluid is limited to a constant volume, well below the rupture volume of the cell. In this way, a hole is formed by compaction by repeated enlargement of each hole section by correspondingly larger penetrating portions.
It is the primary object of the present invention to provide improved means and methods for applying lateral thrust, and in particular to provide improved earth penetrating means and methods. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.